This type of separator superheater comprises a cylindrical shell which rests horizontally on two supports placed near to its ends and which encloses a steam and moisture separator in its lower portion and a steam superheater in its upper portion. The steam and moisture separator is generally constituted by a set of baffle plates. The steam to be processed passes through the baffles on arriving in the separator superheater. The baffles are mounted on a frame which is supported by the shell and which also serve to support the steam superheater. The steam superheater is constituted by one or more heat exchangers which are generally formed by means of hair-pin bend tubes placed on the path of the steam to be processed at the outlet from the steam and moisture separator. The bent tubes are fed with heating steam from a steam chest or steam header which is fixed to the set of tubes by means of a perforated plate or tube sheet and which encloses a heating steam admission chamber and a condensate exhaust chamber connected respectively to a steam inlet duct and to a condensate outlet duct.
If the separator superheater is very heavy, more than about one hundred tons, the steam superheater must be assembled on site and must therefore be capable of being inserted into the shell without requiring major or difficult welding operations to be performed thereon such as welding on a cover covering the full cross section of the shell. In order to do this, some prior art separator superheaters include a running path of rollers on the frame which is to support the steam superheater, thereby enabling the steam superheater to slide longitudinally into the tubular shell. One of the ends of the shell is also fitted with a flanged cover extending over its entire section in order to enable the steam superheater to be inserted therein. In order to avoid the extra cost involved by a large size flanged cover, some prior art separator superheaters have even had end covers welded to the shell in the factory, with one of the end covers being fitted with a loading hatch in line with the running path. The loading patch is fitted with an external sleeve via which the set of steam superheater tubes is inserted. Once in place, the steam chest thereof projects beyond the sleeve and is welded thereto around its periphery.
Since the cross section of the steam chest is much less than that of the shell, the welding is much easier to perform and especially to test than the welding of the end cover to the shell. In order to reduce the cross section of the sleeve and to improve the filling factor of the internal volume of the shell, it is possible to split the steam superheater into two identical portions placed side by side and inserted into the shell via two separate sleeves.
For some high power tubines, it has appeared to be advantageous to use separator superheaters having two superheater stages. This gives rise to assembly problems for the two steam superheat stages since, for reasons of convenience in providing external connections and for reasons of ensuring a high filling factor of the internal volume of the shell, the two stages need to have their steam chests at opposite ends of the shell while still being inserted from the same end so that room to maneuver need only be provided at one end of the shell on site.
Preferred embodiments of the present invention solve this problem while still enabling on-site assembly of steam superheaters in the shell, and consequently making disassembly possible, if required, without damaging the integrity of the shell and without fitting a flanged cover to the end thereof.